| Summary: | A MEMS-based micro-electro-discharge machining technique that is enabled by the
actuation of micromachined planar electrodes defined on the surfaces of the workpiece is
developed that eliminates the need of numerical control machines. First, the planar
electrodes actuated by hydrodynamic force is developed. The electrode structures are
defined by patterning l8-µm-thick copper foil laminated on the stainless steel workpiece
through an intermediate photoresist layer and released by sacrificial etching of the resist layer.
The planer electrodes are constructed to be single layer structures without particular features
underneath. All the patterning and sacrificial etching steps are performed using dry-film
photoresists towards achieving high scalability of the machining technique to large-area
applications. A DC voltage of 80-140 V is applied between the electrode and the workpiece
through a resistance-capacitance circuit that controls the pulse energy and timing of spark
discharges. The parasitic capacitance of the electrode structure is used to form a resistance
capacitance circuit for the generation of pulsed spark discharge between the electrode and the
workpiece. The suspended electrodes are actuated towards the workpiece using the
downflow of dielectric machining fluid, initiating and sustaining the machining process.
Micromachining of stainless steel is experimentally demonstrated with the machining voltage
of 90V and continuous flow of the fluid at the velocity of 3.4-3.9 m/s, providing removal
depth of 20 µm. The experimental results of the electrode actuation match well with the
theoretical estimations. Second, the planar electrodes are electrostatically actuated towards
workpiece for machining. In addition to the single-layer, this effort uses double-layer
structures defined on the bottom surface of the electrode to create custom designed patterns
on the workpiece material. The suspended electrode is electrostatically actuated towards the
wafer based on the pull-in, resulting in a breakdown, or spark discharge. This instantly
lowers the gap voltage, releasing the electrode, and the gap value recovers as the capacitor is
charged up through the resistor. Sequential pulses are produced through the self-regulated
discharging-charging cycle. Micromachining of the stainless-steel wafer is demonstrated
using the electrodes with single-layer and double-layer structures. The experimental results
of the dynamic built-capacitance and mechanical behavior of the electrode devices are also
analyzed.
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